You can do it on a mailbox by mailbox basis - right click on the mailbox in the mailboxes pane and select "Properties" then check the "Set custom preview pane for this mailbox" and choose the "Disabled" radio button. You can make this setting apply to child mailboxes by checking the "Applies to sub-mailboxes" checkbox.

As far as I know there isn't a global option to suppress the preview pane.